The present invention relates to a band-pass filter which comprises at least two quarter-wavelength resonators each having one end thereof open-circuited and the other end thereof short-circuited, and at least two parallel circuit resonators each having a coil and a capacitor.
Conventional band-pass filters comprise within a shielded housing a plurality of juxtaposed quarter-wavelength resonators each comprised of a cylindrical bobbin on which a coil is wound. However, various problems and shortcomings are inherent in the prior art filter. One such shortcoming is that the passband characteristic of the prior art band-pass filter has a gradual decay on each of the cut-off frequency ends. Another shortcoming is that the prior art does not allow compact design.